1. Field of the Invention
The present invention relates to a control apparatus suitable for use in a power window regulator, of a type wherein a window glass is opened and/or closed by making use of an electric motor.
2. Description of the Related Art
There is generally known a control apparatus suitable for use in a power window regulator mounted on a door on the side of a driver's seat of an automobile, to which an auto mode has been set in addition to a normally-used manual mode. In the above-described control apparatus, currents in forward and reverse directions are caused to flow in an electric motor so as to carry out the movement of a window glass in upward and downward directions, and two relays are used so as to form two electrical paths for causing the currents in the forward and reverse directions to flow in the motor.
The actuation of the respective relays in the manual mode is controlled by first and second switching devices (transistors are often used to facilitate control of the relays at the time of the auto mode) which are turned on and off in response to respective operations of a manually-operated window glass move-up switch and a manually-operated window glass move-down switch. More specifically, a first relay is actuated by the first switching device during a period in which the manually-operated window glass move-up switch is turned on so as to form an electrical path for causing the current in the forward direction to flow in the motor. On the other hand, a second relay is actuated by the second switching device during a period in which the manually-operated window glass move-down switch is turned on so as to form an electrical path for causing the current in the reverse direction to flow in the motor. Thus, the window glass is moved upward and downward in the manual mode.
There has been proposed a holding circuit, to be described later, in order to control the actuation of the respective relays at the time of the auto mode. More specifically, the holding circuit has a first capacitor charged immediately when an automatically-operated window glass move-up switch is turned on in a state in which the first relay is actuated (i.e., in a state in which the first switching device is turned on), and a second capacitor charged immediately when an automatically-operated window glass move-down switch is turned on in a state in which the second relay is actuated (i.e., in a state in which the second switching device is turned on). The holding circuit also has a comparing circuit for holding either the first switching device or the second switching device in an on state during a period in which a voltage applied across one of the first and second capacitors is greater in level than a specified voltage. Thus, when either the automatically-operated window glass move-up switch or the automatically-operated window glass move-down switch is first turned on, the first or second switching device is held on even after either the window glass move-up switch or the window glass move-down switch is turned off. As a consequence, the window glass is moved in an upward direction (i.e., in a direction in which the window glass is closed) or in a downward direction (i.e., in a direction in which it is opened) during a period in which either the first or second switching device is held on.
In this case, the holding circuit is incidentally provided with a cut-off circuit activated so as to detect a locked-motor current which flows in the motor. The cut-off circuit serves to rapidly discharge electric charges stored in the first and second capacitors in response to its operation. Thus, when the window glass is moved to a position where it is fully closed or opened, the cut-off circuit is activated to reduce the voltage applied across each of the first and second capacitors to the specified voltage or below in level. Therefore, the comparing circuit serves to release each switching device from being held on, and hence the respective relays are de-actuated correspondingly so as to de-energize the motor. As a consequence, the window glass is automatically stopped in the window glass fully closed or opened position.
The electric charges stored in the first and second capacitors are discharged through resistors in accordance with a relatively long time constant, and a timer function is determined by the discharge of the first and second capacitors. More specifically, unless the cut-off circuit is normally operated, the voltage applied across each of the first and second capacitors is reduced to the specified voltage or lower in level by discharging the first and second capacitors through the resistors after a predetermined period of time elapses. Therefore, the comparing circuit serves to release the switching devices from being held on, thereby de-energizing the motor. As a consequence, the motor can be prevented from being energized over an excessively long time.
Further, when the first switching device is turned on, the electric charge stored in the second capacitor is discharged instantaneously through the first switching device. On the other hand, when the second switching device is turned on, the electric charge stored in the first capacitor is discharged momentarily through the second switching device. As a result, when the manually-operated window glass move-down switch is turned on while the window glass is being moved in the upward direction in the auto mode, the electric charge stored in the first capacitor is discharged instantaneously through the second switching device, thus releasing the second switching device from being held on by the holding circuit so as to stop the movement of the window glass in the upward direction at once. On the other hand, when the manually-operated window glass move-up switch is turned on while the window glass is being moved in the downward direction in the auto mode, the electric charge stored in the second capacitor is discharged immediately through the first switching device, thus releasing the first switching device from being held on by the holding circuit so as to immediately stop the movement of the window glass in the downward direction.
According to the conventional arrangement, there are provided first and second capacitors as components for the timer, which are used to prevent the motor from being abnormally energized, in order to accomplish the function of canceling the movement of the window glass in the upward and downward directions at the time of the auto mode as described above. With this arrangement, the first and second capacitors used have a relatively large capacity to meet the need for an increase in a discharge time constant used for the timer function. However, since such capacitors are large in size and relatively expensive, the control apparatus is enlarged as a whole and subjected to an increase in manufacturing cost when two capacitors having relatively large capacities are required, as in the conventional arrangement. Thus, this inconvenience remains an unsolved problem, the solution of which is an object of the invention.